(1) Field of the Invention
This invention relates to a thermal transfer recording material usable in thermal recording equipments such as thermal printers, thermal facsimiles and the like employing a thermal head.
(2) Description of the Prior Art
Currently, thermal transfer recording materials consisting of a thin substrate and a thermal transfer ink coated on the substrate are in use in thermal printers, thermal facsimiles, etc. to form a clear and durable image on an thermal transfer receiving paper. The mechanism of thermal transfer recording with these recording materials is as follows. That is, on the thermal transfer ink side of a thermal transfer recording material is superimposed an thermal transfer receiving paper. Then, heat is selectively applied to the non-ink side of the recording material with a thermal head synchronously with electric signals, whereby an image is melt- or sublimation-transferred onto the thermal transfer receiving paper. Recording is complete when the thermal transfer recording material and the thermal transfer receiving paper are pulled apart.
The thin substrates used in the above thermal transfer recording materials are required to have such thermal resistance as being able to withstand high temperatures (250.degree. to 350.degree. C.) of thermal heads. It is said that good as such substrates are substrates having no melting point such as a condenser paper, a cellophane paper and the like as well as heat-resistant films having a melting point but capable of withstanding high temperatures of thermal heads such as a polyimide film, a teflon film and the like. Other films such as, for example, a polystyrene film, a polyethylene film, a polypropylene film, a polyvinyl chloride film, a polyvinylidene chloride film, a polyethylene terephthalate film, a polycarbonate film and the like are said to have melting points lower than high temperatures of thermal heads, to melt and stick to thermal heads when printing is made and consequently to cause a so-called "sticking" phenomenon making the movement of thermal heads impossible.
As a countermeasure for such substrates causing the sticking phenomenon, Japanese patent application Kokai (Laid-open) No. 7467/1980 discloses that the side of a substrate coming in contact with a thermal head is provided with a heat-resistant protective film made of one member selected from the group consisting of a silicone resin, an epoxy resin, a melamine resin, a phenolic resin, a fluorine resin, a polyimide resin and a nitrocellulose.
Also, Japanese patent application Kokai (Laid-open) No. 155794/1981 discloses that one side of a plastic film substrate is provided with a sticking prevention layer composed of an inorganic pigment of high lubricity and a thermosetting resin material.
Further, Japanese patent application Kokai (Laid-open) No. 74195/1982 discloses that one side of a plastic film substrate is provided with a sticking prevention layer made of silicon oxide or of a three dimensionally crosslinked product of a polyfunctional (meth)acrylate compound.
However, these countermeasures of providing one side of a substrate with a heat-resistant protective layer or a sticking prevention layer increase production steps of thermal transfer recording materials and incur a higher cost.